The Monsters Know What They're Doing     Dungeons And Dragons original/official source
The Monsters Know What They're Doing 2 (moar)     Dungeons And Dragons (no source link)
Angry Golem (web)     D&D 5e original/official source
OSE Encounter Activity Tables     Any original/official source
Pathfinder 1e Bestiary 1     Pathfinder original/official source
Pathfinder 2e Bestiary 1     Pathfinder original/official source
Monster Codex     Pathfinder original/official source
Monsters Of Porphyra v1     Pathfinder original/official source
Tome Of Horrors Complete     Pathfinder original/official source
Classic Monsters Revisited     Pathfinder original/official source
Lost Lands: Mountains Of Madness     Pathfinder original/official source
Monster Manual     D&D 5e original/official source
Tome Of Horrors 2018     D&D 5e original/official source
Flee, Mortals     D&D 5e (no source link)
Ultimate Bestiary: Revenge Of The Horde     D&D 5e original/official source
Volo's Guide To Monsters     D&D 5e original/official source
Limitless Monsters     D&D 5e original/official source
Monster Monday (web)     D&D 5e original/official source
Monsters Of The Underworld     D&D 5e original/official source
Monster Ecology Anthology     D&D 5e (no source link)
Monster Manual     D&D 4e (no source link)
Dungeons And Dragons Essentials: Monster Vault     D&D 4e (no source link)
Monster Vault: Threats To The Nentir Vale     D&D 4e (no source link)
Dragon Magazine     D&D 2e/3e (no source link)
D&D 2e Monstrous Manual     D&D 2e (no source link)
Scruffy Grognard's Monstrous Manual     D&D 2e (no source link)
AD&D Monster Manual     AD&D 1e (no source link)
13th Age Bestiary     13th Age original/official source
Hacklopedia Of Beasts     Hackmaster original/official source
Old World Bestiary     Warhammer original/official source
QUERP Bestiary     QUERP original/official source
Mystara Adversary Compendium I     Dragon Age original/official source
The Monster Overhaul     OSR (no source link)
Baby Bestiary 2     Any original/official source